The food, pharmaceutical, and chemical industries rely heavily on the use of devices for measuring, sensing, or detecting characteristics of a fluid, such as a liquid containing particles. For example, optical sensors are frequently used to detect characteristics of milk in an effort to determine the amount of a particular component present, such as milkfat or casein. The amount of the component detected or sensed then determines whether the fluid meets a certain criteria before undergoing further processing or whether it is suitable for a particular use (i.e., in the case of milk, whether it is suitable for making a particular type, grade, or variety of cheese). Such devices may also be used for detecting when transitions from one fluid product to another occur in a pipeline (i.e., milk to water) or when a cleaning fluid passing through the pipeline reaches a particular level of optical clarity.
In one type of sensing arrangement, light is transmitted from a remote source to a first optical transmitter projecting directly into the stream of fluid passing through a cylindrical pipe segment forming part of a pipeline. A corresponding light receiver is positioned directly opposite the transmitter for receiving any light passing through the fluid as it flows along the pipeline. A light sensor or photodetector associated with or coupled to the receiver detects the amount of light received and generates a corresponding output signal. Using this output signal, a prediction may be made regarding the type of fluid present and/or the amount of a particular substance (e.g., milkfat particles, casein, etc.) in the fluid moving through the pipeline.
While this “transmision” type of sensor arrangement generally permits taking of the desired measurements in an acceptable manner, there are several well-recognized limitations. One significant limitation is that the transmitter and receiver typically project transversely into the fluid flow from the outer wall of the pipeline. Of course, this positioning severely disrupts the fluid flow and may have a deleterious effect on the sensing accuracy. The large physical distance (path length) also limits transmission measurements to relatively clear fluids. Meaningful measurements with whole milk, cream, and other thick fluids cannot be made with the typical transmission sensor. This problem has been addressed by firms such as Wedgewood and Daritek by fabricating lenses that protrude into the fluid. Daritek lists an optical path length (OPC) of 5, 100, and 20 millimeters for their sensor, and Wedgewood explains that custom path lengths are available. However, one of the technical problems with a protruding optical means having a short path length is stability. For example, vibrations, and especially thermal movement of the wall, results in relatively large displacement in the path length. This increases signal error, especially in highly turbid fluids. The protrusion of an optical means into the flow stream may also inhibit fluid flow.
In an effort to prevent this disruption, others have proposed positioning one or more lenses in the outer wall of the pipeline to separate the transmitter and receiver from the fluid flow. However, this increases the path length and complicates the arrangement. Perhaps more importantly, it also prevents the light path distance between the transmitter and the receiver from being easily adjusted.
Accordingly, a need is identified for an improved apparatus for use in measuring, sensing, or detecting a characteristic of a fluid. The apparatus would be inexpensive to manufacture and would be readily adaptable for use with existing fluid vessels, containers, or pipelines. Furthermore, it would allow for the adjustable positioning of one or more devices or units for transmitting/receiving energy to the fluid without creating any significant disturbance therein. Moreover, the apparatus would allow for mounting of the transmitter/receiver in not only a backscatter or transmission configuration, but also in a sidescatter configuration. This would possibly allow for more precise measurements to be taken, including in dense fluids. Overall, the apparatus would result in a significant improvement in terms of reliability and ease of use, especially as compared to the prior art optical sensing arrangement described above.